Problem : 10-5=?

• Let left = 10
• Let right = 5
• Let operator = - (subtraction)
• Solve for ?

Variables or identifiers

• Begin
• Declare x as an integer
• Declare y as an integer
• Declare z as an integer

In ram the "post box" contains x, z and y. All of them are in different containers

• Set x = 10
• Set y = 5

No in the "post boxes" x and y are equal to 10 and 5. X and y now point to the numbers they are supposed to represent.

• Set z = x-y (you substituted the numbers for their variables)
• Display x-y= z

We can now do another problem with the same variables

• P = Z * 2
• P is a null value
• It does not stand for anything

P is now displayed as a null variable in RAM. When the computer solves the problem p then turns to point to 10.

• End the problem

Terminology

• Bin -
• Identifier in memory which points to a values
• Null -
•  A thing with no value

Contd.

• Variables are stored in RAM as hexadecimal addresses.
• You have to always define the variables
• Integers always have a value
• An integers range is -2 147 483 684 to 2 147 483 647
• For something to have a value in RAM it has to point to something
• Addresses have 16 digits
• In programming we are
• Mimicking real life objects in a computer environment
• People
• Buildings
• Cars
• Money
• Working rates
• Tax

Variables in Memory

• A address can only hold one variable
• When you add a new value to a variable it over-rides the original one.
• X=10
• X=20
• X=x+10
• X changes value every time here
• The equals sign represents an assignment operator
• The signs that we use
• +
• -
• Subtraction
• *
• Multiplication
• /
• Division
• %
• Modulus
• The remainder of your division
• !
• Not
• =
• Assignment operator
• >=
• Greater than or equal to
• <=
• Less than or equal to
• ==
• Equality

• When we manipulate x we manipulate the value in ram

Data Types

• Three common data types are used
• Integer
• Can store only whole numbers
• Floating point numbers
• Can store numbers with fractional values
• Character
• Can store a character
• String
• Character
• Examples
• Age
• Integer
• Money
• Floating point
• Gender
•  Character
• Alphanumeric
• Surname
• String
• De Beer
• Phone number
• String
• 011 465 7654
• Date
• String
• 07/04/2015

• If you are not going to use something in an expression, it is alphanumeric
• Strings are multiple character values
• When there is a single quotation mark it is a character
• When there are two quotation marks then it is a collection of characters
• Characters are for one character
• A bit is a 0 or 1
• One of them indicate on and the other off
• 8 bits make a byte
• 16 bits = 2 bytes
• 32 bits = 4 bytes
• 64 bits = 8 bytes